Summary/abstract Tubulointerstitial fibrosis, a common endpoint outcome of a wide range of chronic kidney diseases (CKD), typically initiates at certain focal sites, in which interstitial fibroblasts become activated, proliferate and produce a large amount of extracellular matrix. This competitive renewal application proposes to delineate the role of tenascin C (TNC), a matricellular protein, in orchestrating the formation of fibrogenic microenvironment in kidney fibrosis. Studies in previous project period of this application indicate that TNC is induced rapidly in the early stage of kidney injury and predominantly localizes at the foci rich in fibroblasts. TNC is able to promote renal interstitial fibroblast proliferation in vitro, ex vivo and in vivo. Intriguingly, TNC binds to, recruits and concentrates sonic hedgehog (Shh) and Wnt ligands from surrounding milieu. Based on these observations, the central hypothesis of this application is that TNC organizes a profibrotic microenvironment in which Shh and Wnts are enriched, thereby setting a unique stage facilitating fibroblast activation and proliferation, as well as aggravating tubular injury and inflammation. We will test this hypothesis in three specific aims. Aim 1 is to investigate the role of TNC in establishing fibrogenic microenvironment by recruiting, concentrating and presenting Wnt and Shh ligands. Aim 2 is to investigate the role of injured tubules and activated macrophages in building the fibrogenic niche, and to investigate the role of TNC-rich niche in aggravating tubular injury and inflammation. Aim 3 is to evaluate the therapeutic efficiency of disrupting TNC-enriched microenvironment for treatment of fibrotic CKD. These studies promise to offer novel insights into understanding the role of TNC in organizing a profibrotic microenvironment. The concept that the TNC-rich microenvironment, in which fibrotic factors are recruited and enriched, plays a critical role in renal fibrogenesis represents a new paradigm in our understanding of kidney fibrosis. Undoubtedly, the data generated from this application will have wide implications in comprehending the pathogenesis of tissue fibrosis in general and kidney fibrosis in particular, as well as in designing future therapeutic regimens for treatment.